The transmission of viral hepatitis by plasma derivatives continues to be an important medical problem that has been made more urgent by the similar epidemiology of the putative agent of acquired immune deficiency syndrome. Methods of inactivating viruses in plasma derivatives while retaining the biological potency of the products are being explored. These include the application of heat to lyophilized biological products and extraction of lyophilized or aqueous preparations with lipid solvents such as chloroform.